Basically it depends upon what specific major you will be studying in the US. Even in Liberal Arts there are variety of courses that you can pick apart from chemistry, however, you need to understand that studying Chemistry in A Levels is as competitive as studying Computer Science and Further Maths. I advise you to ask yourself once whether you can labor and improve your grades or not. There are many students who uplifted themselves from the poorest grades to “A”,as far as concerned in Chemistry. It would be better if you do not leave chemistry at least for A-Levels. But if you are really screwed up, don’t think anything and directly drop it. You should be happy with your half-credits.
If you do not like Chemistry and are not going to pursue it in uni you may drop it. It’s better to get good grades in easier subjects than to get bad grades at harder ones. Just study what you like and don’t worry too much.
If you have any more queries feel free to ask a follow up question.